1. Field of the Invention
This invention regards the field of single-phase rotating electromagnetic actuators, that is, electromagnetic devices that have a limited stroke, as opposed to engines that have an unlimited stroke. Actuators are designed for precise positioning, with good repeatability, of an associated mechanism, with constant torque throughout the length of the stroke with a simple control law, preferably linear, avoiding the use of complex control circuits.
2. Discussion of the Background
In the current state of the art there are many types of rotating single-phase actuators that comprise a stationary component consisting of a first stator magnetic circuit made of a material with very high magnetic permeability energized by at least one energizer coil and a mobile component consisting of an axially magnetized disk.
For example, American patent U.S. Pat. No. 4,510,403 describes an actuator comprising a thick central magnet. Such actuators do not supply constant torque, and have central position restoring torque.
In general, we know how to eliminate these disadvantages by using thin magnets transversely magnetized in the direction of the smallest dimension, perpendicular to the polar surfaces. This magnetized disk has 2N pairs of magnetic poles magnetized in alternating directions. The magnetization is virtually uniform. The magnetized disk is attached to a second magnetic circuit made of a material with high magnetic permeability. The mobile component is equipped with a coupling shaft designed to transmit the torque.
By way of example, these types of actuators are described in French patent application EP558362 filed by the applicant.
These actuators have constant torque for a given current, and a torque proportional to the current applied to the energizer coil. However, they have one disadvantage concerning their price: they require high energy magnets, Neodymium-Iron-Boron magnets, for example, whose cost price is high.
Additionally, the structures of the prior art use multipolar magnets or assemblies of several magnets in alternating direction, which prohibits magnetizing after assembly and requires handling high energy magnets when the actuators are being assembled. This type of handling is delicate, since high energy magnets can introduce particles, metal shavings, for example, into the actuators when they are positioned on the mobile component. To prevent this disadvantage, we know how to encapsulate the magnets, a costly solution that has the disadvantage of further increasing the cost price of the actuators.